center portion of the area becomes filled. The following sand and 

 grains are then forced to move over the groin tops (which are now 

 flush with the built-up sand bed) and seaward of the structures. 

 This essentially causes the beach face to be moved seaward and, after 

 a time, the groins are completely buried beneath the sand and the new 

 beach is relocated further seaward. The behavior of the beach appears 

 to be predominately dependent upon the transport rate as to whether 

 the body of the beach face is to remain in a stabilized state or not. 



In order to observe the path that the littoral current takes 

 through the permeable groins, a dye was introduced in the breaker-to- 

 shore region where the probable maximum littoral velocity occurs. 

 The results were indicative of where the sand usually builds up and/ 

 or scours around the groins, as determined from the other experiments. 

 The fact that the dye went through the first two groins in an even 

 n fan m pattern would tend to show that the littoral current was still 

 great enough to also carry the sand particles through the slat section. 

 Furthermore, it would tend to indicate that should permeable groins be 

 contemplated for a comparable prototype situation, they should be used 

 in groups of three or more groins. 



In tests made to study the bed load movement of the sand particles 

 in the breaker region, the sand grains were observed generally to follow 

 a definite pattern. The initial wave action first covered the grains 

 in the bed, then the following waves uncovered the grains and moved them 

 a short distance in both a seaward and lateral direction. Succeeding 

 waves again covered the particles and the process began to be repeated. 

 The cycle occurred within approximately 1 minute (60 waves for this 

 particular test). This cyclic particle movement also has been observed 

 in the one-foot wave channel as discussed in Section "A 1 * above. 



The Movement of Sand Transported by Wave Action Along a Straight Beach 



Waves breaking at an angle to a beach generate a current that 

 moves parallel to the beachj this is known as the littoral current. 

 The purpose of this investigation was to study to what extent a change 

 in wave characteristics and beach affected the rate of transportation. 

 The experimental program began with a continuation of previous ex- 

 periments on sand transport.* A wave machine and a model beach were 

 arranged in a model basin approximately 66 ft. by 122 ft. in plan and 

 two feet in depth. The wave machine was of the flap type in which the 

 period of the waves could be varied by changing the speed of the driving 

 motor, and the wave energy could be changed by adjusting the throw on 

 crank arms connected to the wave flaps. The wave height and wave 

 length were determined by the period and energy settings. A sand beach 

 was molded initially to a l/lO slope by screeding, and then allowed 

 to develop its profile under the action of the waves. A sand trap and 



■frSaville, Thorndike, Jr. 3 Model Study of Sand Transport Along an In- 

 finitely Straight Beach, Trans. Amer. Geoph. Union, Vol. 31, 1950 



